Production of 1,2-dihydro and 2,2-dihydro hexafluoropropanes and azeotropes thereof with HF

ABSTRACT

CF 3 CHFCHF 2  production is disclosed which involves reacting CF 3 CF═CHF with HF at an elevated temperature over a catalyst selected from the group consisting of aluminum fluoride, fluorided alumina, metals supported on aluminum fluoride, metals supported on fluorided alumina and catalysts comprising trivalent chromium. Also disclosed is enrichment of CF 3 CF═CHF from a starting mixture containing CF 3 CF═CHF and CF 3 CH═CF 2  which involves reacting said starting mixture with HF at an elevated temperature over a catalyst consisting essentially carbon, a catalyst consisting essentially of metal halides supported on carbon, a catalyst consisting essentially of Cr 2 O 3 , or mixtures thereof (provided that when Cr 2 O 3  is present the temperature is about 250° C. or less) to produce a product mixture containing CF 3 CH 2 CF 3  and unreacted CF 3 CF═CHF wherein the mole ratio of CF 3 CF═CHF to CF 3 CH═CF 2  is greater than the ratio thereof in the starting mixture.  
     Compositions are disclosed which consist essentially of hydrogen fluoride in combination with an efective amount of a compound selected from the group consisting of CF 3 CHFCHF 2  and CF 3 CH 2 CF 3  to form an azeotrope or azeotrope-like composition with hydrogen fluoride. Included are compositions containing from about 31 to 60 mole percent CF 3 CHFCHF 2  and compositions containing from about 41 to 63 mole percent CF 3 CH 2 CF 3 .

FIELD OF THE INVENTION

[0001] This invention relates to the manufacture of hydrofluorocarbons(i.e., HFCs) and azeotropic compositions thereof, and more particularlyto the production of hexafluoropropanes and their azeotropiccompositions with HF.

BACKGROUND

[0002] 1,1,1,2,3,3-hexafluoropropane (i.e., CHF₂CHFCF₃ or HFC-236ea) and1,1,1,3,3,3-hexafluoropropane (i.e., CF₃CH₂CF₃ or HFC-236fa) are usefulas refrigerants, fire extinguishants, heat transfer media, gaseousdielectrics, sterilant carriers, polymerization media, particulateremoval fluids, carrier fluids, buffing and abrasive agents,displacement drying agents and power cycle working fluids. Inparticular, HFC-236ea and HFC-236fa are highly effective as refrigerantsfor use in refrigeration equipment.

[0003] U.S. Pat. No. 5,171,901 discloses a process for the preparationof HFC-236fa by contacting a mixture of hexachloropropene and HF with acatalyst consisting of a mixture of CrCl₃ and MgF₂ at temperaturesranging from 350° C. to 500° C. The reaction temperatures and yields ofHFC-236fa were as follows: 350° C., none detected; 400° C., 10%; 450°C., 55%; and 500° C., 64%. Other products formed in varying amounts wereCF₃CHClCF₃, CF₃CCl₂CF₃, CF₃CCl═CF₂, CF₃CCl═CClF, and CF₃CCl═CCl₂.HFC-236ea has been prepared by the hydrogenation of hexafluoropropane.There is an interest in developing additional, efficient processes forthe manufacture of HFC-236ea and HFC-236fa from various startingmaterials.

SUMMARY OF THE INVENTION

[0004] This invention provides a process for producing CF₃CHFCHF₂. Thisprocess comprises reacting CF₃CF═CHF with HF at an elevated temperatureover a catalyst selected from the group consisting of aluminum fluoride,fluorided alumina, metals supported on aluminum fluoride, metalssupported on fluorided alumina and catalysts comprising trivalentchromium. Also provided is a process for enriching CF₃CF═CHF from astarting mixture containing CF₃CF═CHF and CF₃CH═CF₂. This processcomprises reacting said starting mixture with HF at an elevatedtemperature over a catalyst consisting essentially of carbon, a catalystconsisting essentially of metal halides supported on carbon, a catalystconsisting essentially of Cr₂O₃, or mixtures thereof (provided that whenCr₂O₃ is present the temperature is about 250° C. or less) to produce aproduct mixture containing CF₃CH₂CF₃ and unreacted CF₃CF═CHF wherein themole ratio of CF₃CF═CHF to CF₃CH═CF₂ is greater than the ratio thereofin the starting mixture. This invention provides for production ofCF₃CH₂CF₃ (or both CF₃CFHCHF₂ and CF₃CH₂CF₃) by reacting a startingmixture containing both CF₃CF═CHF and CF₃CH═CF₂ with HF at an elevatedtemperature over a fluorination catalyst.

[0005] This invention further provides compositions which consistessentially of hydrogen fluoride in combination with an efective amountof a compound selected from the group consisting of CF₃CHFCHF₂ andCF₃CH₂CF₃ to form an azeotrope or azeotrope-like composition withhydrogen fluoride, said composition containing from about 31 to 60 molepercent CF₃CHFCHF₂ or from about 41 to 63 mole percent CF₃CH₂CF₃.

DETAILED DESCRIPTION

[0006] The addition of hydrogen fluoride across the double bond ofolefinic compounds normally follows Markovnikov's rule (i.e., hydrogenis added to the carbon atom of the double bond which has a hydrogenatom, and fluorine to the olefinic carbon atom which has a fluorineatom). U.S. Pat. No. 5,268,122 provides examples of Markovnikov additionto olefinic fluoro-carbon bonds. In accordance with this invention, HFadds across the double bond of CF₃CF═CHF to produce CHF₂CHFCF₃ ratherthan the Markovnikov expected product, CH₂FCF₂CF₃. Thus, this inventionprovides a process which involves reacting CF₃CF═CHF with HF to add H atthe olefinic carbon different from the olefinic carbon alreadycontaining a hydrogen such that CF₃CFHCHF₂ is produced.

[0007] CF₃CF═CHF can be prepared according to R. N. Hazeldine et al., J.Chem. Soc. Perkin Trans.1, 1303-07 (1974). CF₃CF═CHF may. also beproduced from CF₃CF₂CH₂F (i.e., HFC-236cb) by dehydrofluorination (e.g.,by reacting CF₃CF₂CH₂F with KOH). Because of this unexpected chemistry,HFC-236cb can be converted to HFC-236ea by first dehydrofluorinatingHFC-236cb to CF₃CF═CHF and then reacting the CF₃CF═CHF with HF to affordHFC-236ea. Accordingly, this invention provides a process for producingCF₃CHFCHF₂ from its isomer CF₃CF₂CH₂F by dehydrofluorinating CF₃CF₂CH₂Fto CF₃CF═CHF, and reacting CF₃CF═CHF with HF to provide CF₃CHFCHF₂.

[0008] Preferred catalysts for the reaction of CF₃CF═CHF with HF includealuminum fluoride, fluorided alumina, metals supported on aluminumfluoride, metals supported on fluorided alumina and catalysts containingtrivalent chromium. Suitable metals (including metal oxides, metalhalides and/or other metal salts) for use on aluminum fluoride orfluorided alumina include (in addition to trivalent chromium) Group VIIImetals (iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium,iridium, platinum), Group VIIB metals (manganese, rhenium), Group IIIBmetals (scandium, yttrium, lanthanum), Group IB metals (copper, silver,gold), zinc and/or metals having an atomic number of 58 through 71(cerium, praseodymium, neodymium, promethium, samarium, europium,gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, orlutetium). Preferably the total metal content of the catalyst will befrom about 0.1 to 20 percent by weight; typically from about 0.1 to 10percent by weight of the supported catalyst. It is understood that incatalyst preparation a metal compound may be supported on an alumina,and the resulting supported metal composition may then be fluorinated.Especially preferred for the reaction of CF₃CF═CHF are chrome oxidecatalysts prepared by the pyrolysis of ammonium dichromate (see U.S.Pat. No. 5,036,036 for preparative details).

[0009] Typically the temperature for the reaction of CF₃CF═CHF is fromabout 275° C. to 450° C. Temperatures between 300° C. and 400° C. aregenerally preferred.

[0010] A process for production of CF₃CH₂CF₃ is also provided by thisinvention. CF₃CH₂CF₃ may be produced by reacting CF₃CH═CF₂ in a startingmixture containing CF₃CH═CF₂ and CF₃CF═CHF with HF to add H at theolefinic carbon already containing a hydrogen. Fluorination catalystsare used for this reaction. Preferably, the mole ratio of CF₃CH═CF₂ toCF₃CF═CHF in the starting mixture is from 5:95 to 95:5.

[0011] Suitable catalysts which can be used for reacting CF₃CH═CF₂ withHF to produce CF₃CH₂CF₃ include vapor phase fluorination catalysts.Catalysts which may be used in accordance with this invention includemetals (including metal oxides, metal halides and/or other metal salts);fluorided alumina; aluminum fluoride; metals on aluminum fluoride;metals on fluorided alumina; metals on carbon; and chromium catalysts.Suitable metals for use in such catalysts include chromium, Group VIIImetals (iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium,iridium, platinum), Group VIIB metals (manganese, rhenium), Group IIIBmetals (scandium, yttrium, lanthanum), Group IB metals (copper, silver,gold), zinc and/or metals having an atomic number of 58 through 71(cerium, praseodymium, neodymium, promethium, samarium, europium,gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, orlutetium). Preferably, when used on a support, the total metal contentof the catalyst will be from about 0.1 to 20 percent by weight;typically from about 0.1 to 10 percent by weight.

[0012] Fluorided alumina and aluminum fluoride can be prepared asdescribed in U.S. Pat. No. 4,902,838. Metals on aluminum fluoride andmetals on fluorided alumina can be prepared by procedures described inU.S. Pat. No. 4,766,260. Catalysts comprising chromium are well known inthe art, e.g., see U.S. Pat. No. 5,036,036. Chromium supported onalumina can be prepared as described in U.S. Pat. No. 3,541,165.Chromium supported on carbon can be prepared as described in U.S. Pat.No. 3,632,834. Preferred catalysts include aluminum fluoride, fluoridedalumina, catalysts comprising carbon and catalysts comprising chromiumoxide.

[0013] Typically, the temperature for the reaction of CF₃CH═CF₂ is fromabout 150° C. to 450° C. Temperatures between 175° C. and 400° C. aregenerally preferred. It is noted that suitable catalysts include thoselisted above for the reaction of CF₃CF═CHF with HF. When these catalystsare used at sufficiently high temperatures, the product containsCF₃CFHCHF₂ along with CF₃CH₂CF₃.

[0014] In accordance with this invention, catalysts selected from thegroup consisting of (1) catalysts consisting essentially of carbon, (2)catalysts consisting essentially of metal halides supported on carbon,(3) catalysts consisting of Cr₂O₃, and mixtures thereof, may be usedsuch that CF₃CH═CF₂ is selectively reacted with HF and the reactionproduct contains CF₃CH₂CF₃ and unreacted CF₃CF═CHF from the startingmixture. Suitable metal halides include chlorides and fluorides ofchromium, nickel, cobalt, zinc, copper, iron and/or manganese.Especially preferred are carbon catalysts which have an ash content ofless than about 0.1 percent by weight (see U.S. Pat. No. 5,136,113 forpreparative details). The selective reaction of CF₃CH═CF₂ with HF may beused to provide enriched CF₃CF═CHF from a mixture of CF₃CF═CHF andCF₃CH═CF₂. The selective reaction of CF₃CH═CF₂ is normally conducted ata temperature within the range of about 150° C. to 350° C. (preferablybetween about 200° C. and 300° C.); except that when Cr₂O₃ is presentthe temperature should normally be about 250° C. or less.

[0015] If desired, the CF₃CH₂CF₃ produced by selective reaction ofCF₃CH═CF₂ may be separated by conventional processes (e.g.,distillation) from the unreacted CF₃CF═CHF, and the CF₃CF═CHF may thenbe reacted with HF as described above to form CF₃CHFCHF₂ in anadditional step. Accordingly, a process for producing CF₃CHFCHF₂ isprovided which also produces CF₃CH₂CF₃ comprises reacting a startingmixture comprising CF₃CH═CF₂ and CF₃CF═CHF with HF at an elevatedtemperature using a catalyst consisting essentially of carbon, acatalyst consisting essentially of metal halides supported on carbon, acatalyst consisting essentially of Cr₂O₃, or mixtures thereof (providedthat when Cr₂O₃ is present the temprature is about 250° C. or less) toprovide a product mixture containing CF₃CH₂CF₃ and unreacted CF₃CF═CFH;separating CF₃CH₂CF₃ from CF₃CF═CHF in the product mixture; and reactingCF₃CF═CHF from the product mixture with HF at an elevated temperatureover a catalyst selected from the group consisting of aluminum fluoride,fluorided alumina, metals on aluminum fluoride, metals on fluoridedalumina and catalysts containing trivalent chromium to produceCF₃CHFCHF₂. CF₂═CHCF₃ can be prepared according to P. Tarrant et al., J.Am. Chem. Soc., 77, 2783-7 (1955).

[0016] It is noted that at temperatures of about 250° C. or less, Cr₂O₃catalyst may be advantageously used for the selective reaction ofCF₃CH═CF₂ from a mixture containing CF₃CH═CF₂ and CF₃CF═CHF to provide aproduct mixture containing CF₃CH₂CF₃ and unreacted CF₃CF═CHF; whereas athigher temperatures Cr₂O₃ catalyst more readily provides reaction ofboth CF₃CH═CF₂ and CF₃CF═CHF. Accordingly, two reaction zonessequentially operating at a temperature of about 250° C. or less, and ata temperature above 250° C. may be used to sequentially convertCF₃CH═CF₂ and then CF₃CF═CHF.

[0017] The molar ratio of HF to the C₃HF₅ olefin or mixture of olefinsbeing reacted typically ranges from about 1:1 to about 100:1, and ispreferably within the range of about 1:1 to about 4:1. The contact timeis typically from about 1 to about 100 seconds.

[0018] 1,1,1,3,3,3-Hexafluoropropane and/or1,1,1,2,3,3-hexafluoropropane may be recovered from the reactionproducts by using conventional techniques such as decantation anddistillation.

[0019] The process of this invention can be carried out readily in thevapor phase using well known chemical engineering practice.

[0020] The reaction zone and its associated feed lines, effluent linesand associated units should be constructed of materials resistant tohydrogen fluoride. Typical materials of construction, well-known to thefluorination art, include stainless steels, in particular of theaustenic type, the well-known high nickel alloys, such as Monel®nickel-copper alloys, Hastelloy® nickel-based alloys and, Inconel®nickel-chromium alloys, and copper-clad steel. Also suitable for reactorfabrication are such polymeric plastics as polytrifluorochloroethyleneand polytetrafluoroethylene, generally used as linings.

[0021] The present invention also provides compositions which consistessentially of hydrogen fluoride and an effective amount of a compoundselected from CF₃CH₂CF₃ and CHF₂CHFCF₃ to form an azeotropic combinationwith hydrogen fluoride. By effective amount is meant an amount which,when combined with HF, results in the formation of an azeotrope orazeotrope-like mixture. As recognized in the art, an azeotrope or anazeotrope-like composition is an admixture of two or more differentcomponents which, when in liquid form under given pressure, will boil ata substantially constant temperature, which temperature may be higher orlower than the boiling temperatures of the individual components, andwhich will provide a vapor composition essentially identical to theliquid composition undergoing boiling.

[0022] An azeotrope is a liquid mixture that exhibits a maximum orminimum boiling point relative to the boiling points of surroundingmixture compositions. An azeotrope is homogeneous if only one liquidphase is present. An azeotrope is heterogeneous if more than one liquidphase is present. Regardless, a characteristic of minimum boilingazeotropes is that the bulk liquid composition is then identical to thevapor composition in equilibrium therewith, and distillation isineffective as a separation technique. For the purpose of thisdiscussion, azeotrope-like composition means a composition which behaveslike an azeotrope (i.e., has constant-boiling characteristics or atendency not to fractionate upon boiling or evaporation). Thus, thecomposition of the vapor formed during boiling or evaporation of suchcompositions is the same as or substantially the same as the originalliquid composition. Hence, during boiling or evaporation, the liquidcomposition, if it changes at all, changes only to a minimal ornegligible extent. This is to be contrasted with non-azeotrope-likecompositions in which during boiling or evaporation, the liquidcomposition changes to a substantial degree.

[0023] Accordingly, the essential features of an azeotrope or anazeotrope-like composition are that at a given pressure, the boilingpoint of the liquid composition is fixed and that the composition of thevapor above the boiling composition is essentially that of the boilingliquid composition (i.e., no fractionation of the components of theliquid composition takes place). It is also recognized in the art thatboth the boiling point and the weight percentages of each component ofthe azeotropic composition may change when the azeotrope orazeotrope-like liquid composition is subjected to boiling at differentpressures. Thus an azeotrope or an azeotrope-like composition may bedefined in terms of the unique relationship that exists among componentsor in terms of the compositional ranges of the components or in terms ofexact weight percentages of each component of the compositioncharacterized by a fixed boiling point at a specified pressure. It isalso recognized in the art that various azeotropic compositions(including their boiling points at particular pressures) may becalculated (see, e.g., W. Schotte, Ind. Eng. Chem. Process Des. Dev.1980, 19, pp 432-439). Experimental identification of azeotropiccompositions involving the same components may be used to confirm theaccuracy of such calculations and/or to modify the calculations forazeotropic compositions at the same or other temperatures and pressures.

[0024] Compositions may be formed which consist essentially ofazeotropic combinations of hydrogen fluoride with a compound selectedfrom CF₃CH₂CF₃ and CHF₂CHFCF₃. These include a composition consistingessentially of from about 40 to about 69 mole percent HF and from about31 to 60 mole percent CHF₂CHFCF₃ (which forms an azeotrope boiling at atemperature from between about −25° C. and about 100° C. and a pressurebetween about 32 kPa and about 2500 kPa); and a composition consistingessentially of from about 37to about 59 mole percent HF and from about41 to about 63 mole percent CF₃CH₂CF₃ (which forms an azeotrope boilingat a temperature between about −25° C. and 100° C. and a pressurebetween about 44 kPa and about 2900 kPa).

[0025] At atmospheric pressure, the boiling points of hydrofluoric acid,HFC-236ea and HFC-236fa are about 19.5° C., 6° C. and −0.7° C.,respectively. However, the relative volatility at 234 kPa (34 psia) and20° C. of HF and HFC-236ea was found to be nearly 1.0 as 56 mole percentHF and 44 mole percent HFC-236ea was approached; and the relativevolatility at 294 kPa (42.7 psia) and 20° C. of HF and HFC-236fa wasfound to be nearly 1.0 as 50 mole percent HF and 50 mole percentHFC-236fa was approached. These data indicate that the use ofconventional distillation procedures will not result in the separationof a substantially pure compound because of the low value of relativevolatility of the compounds.

[0026] To determine the relative volatility of HF with each of HFC-236eaand HFC-236fa, the so-called PTx Method was used. In this procedure, thetotal absolute pressure in a cell of known volume is measured at aconstant temperature for various known binary compositions. Use of thePTx Method is described in greater detail in “Phase Equilibrium inProcess Design”, Wiley-Interscience Publisher, 1970, written by HaroldR. Null, on pages 124 to 126.

[0027] These measurements can be reduced to equilibrium vapor and liquidcompositions in the cell by an activity coefficient equation model, suchas the Non-Random, Two-Liquid (NRTL) equation, to represent liquid phasenon-idealities. Use of an activity coefficient equation, such as theNRTL equation, is described in greater detail in “The Properties ofGases and Liquids”, 4th Edition, publisher McGraw Hill, written by Reid,Prausnitz and Poling, on pages 241 to 387; and in “Phase Equilibria inChemical Engineering”, published by Butterworth Publishers, 1985,written by Stanley M. Walas, pages 165 to 244.

[0028] Without wishing to be bound by any theory or explanation, it isbelieved that the NRTL equation can sufficiently predict whether or notmixtures of HF and any of HFC-236ea and HFC-236fa behave in an idealmanner, and can sufficiently predict the relative volatilities of thecomponents in such mixtures. Thus, while HF has a good relativevolatility compared to HFC-236ea at low HFC-236ea concentrations, therelative volatility becomes nearly 1.0 as 44 mole percent HFC-236ea wasapproached at 20° C. This would make it impossible to separate HFC-236eafrom HF by conventional distillation from such a mixture. Where therelative volatility approaches 1.0 defines the system as forming anear-azeotrope. Where the relative volatility is 1.0 defines the systemas forming an azeotrope.

[0029] It has been found that azeotropes of HF and HFC-236ea are formedat a variety of temperatures and pressures. At a pressure of 34 psia(234 kPa) and 20° C., the azeotrope vapor composition was found to beabout 56 mole percent HF and about 44 mole percent HFC-236ea. Based uponthe above findings, it has been calculated that an azeotropiccomposition of about 69 mole percent HF and about 31 mole percentHFC-236ea can be formed at −25° C. and 4.7 psia (32 kPa) and anazeotropic composition of about 40 mole percent HF and about 60 molepercent HFC-236ea can be formed at 100° C. and 363 psia (2500 kPa).Accordingly, the present invention provides an azeotrope orazeotrope-like composition consisting essentially of from about 69 to 40mole percent HF and from about 31 to 60 mole percent HFC-236ea, saidcomposition having a boiling point from about −25° C. at 32 kPa to about100° C. at 2500 kPa.

[0030] It has been found that azeotropes of HF and HFC-236fa are formedat a variety of temperatures and pressures. At a pressure of 42.7 psia(about 294 kPa) and 20° C., the azeotrope vapor composition was found tobe about 50 mole percent HF and about 50 mole percent HFC-236fa. Basedupon the above findings, it has been calculated that an azeotropiccomposition of about 37 mole percent HF and about 63 mole percentHFC-236fa can be formed at 100° C. and 422 psia (2900 kPa). Accordingly,the present invention provides an azeotrope or azeotrope-likecomposition consisting essentially of from about 59 to 37 mole percentHF and from about 31 to 63 mole percent HFC-236fa, said compositionhaving a boiling point from −25° C. at about 44 kPa to about 100° C. atabout 2900 kPa.

[0031] The HFC-236ea/HF and HFC-236fa/HF azeotropes are useful as feedto produce HFC-227ca (CHF₂CF₂CF₃) and/or HFC-227ea (CF₃CHFCF₃) (see U.S.Pat. No. 5,177,273). It will also be apparent to one of ordinary skillin the art that distillation including azeotropes with HF can typicallybe run under more convenient conditions than distillation without HF(e.g., where HF is removed prior to distillation).

[0032] Practice of the invention will become further apparent from thefollowing non-limiting examples.

EXAMPLES

[0033] General Evaluation Procedure

[0034] A reactor, 11″ (27.9 cm)×½″ (1.3 cm) Inconel® nickel alloy tube,containing an internal thermowell, containing from about 12 to 15 mL ofcatalyst (10 to 14 mesh, i.e., about 1.7 to 1.3 mm), was heated in afluidized sandbath. The feed to the reactor was measured through massflow controllers. The organic feed was mixed with HF prior to enteringthe reactor. All examples were performed at ambient pressure. Theproducts from the reactor were analyzed by on line GC/MS. The gaschromatograph was a Hewlett Packard HP 5890 containing a 20 foot (6.1 m)long, one-eighth inch (0.32 cm) diameter column containing Krytox®, aperfluorinated polyether on an inert support. The helium flow rate was35 mL/minute. GC results are reported in mole %.

[0035] Activation of Carbon-Based Catalysts

[0036] The reactor was charged with the catalyst and heated to 300° C.in a flow of nitrogen (25 mL/min) for about 2 hours. The temperature wasreduced to 175° C. and a 2:1 molar ratio of nitrogen and HF was startedthrough the reactor (total flow 100 mL/min). After about one hour underthese conditions, the molar ratio of nirogen to HF was adjusted to 1:3and the temperature gradually increased over a two hour period to 400°C. The reactor was then brought to the desired operating temperature,the nitrogen flow stopped, and the flow of reactants started.

[0037] Activation of Chromium Oxide

[0038] The reactor was charged with chromium oxide and heated to about175° C. for about two hours in a flow of nitrogen (25 mL/min). At theend of this period, a flow of nitrogen and HF in the molar ratio of 2:1(total flow 100 mL/min) was started through the reactor. After aninitial exotherm of about 10 to 30 degrees subsided, the molar ratio ofnitrogen to HF was adjusted to 1:3 and the temperature graduallyincreased over a three hour period to 400° C. The reactor and contentswere kept at this temperature for about an additional 30 minutes andbrought back to the desired operating temperature. The nitrogen flow wasstopped and the flow of reactants started.

Example 1

[0039] Reaction of CF₃CF═CFH with HF

[0040] The reactor was charged with 19.5 g of chromium oxide which wasactivated according to the procedure described above. A flow of HF andCF₃CF═CFH in a 4:1 molar ratio was started through the reactor. Thecontact time was 30 seconds. The organic feed contained 85.3% CF₃CF═CFHand 13.6% trifluoroethylene in addition to small amounts of othercomponents. Product analysis indicated the following. Temp. ° C. CF₃CH₂FCF₃CF═CFH CF₃CHFCHF₂ 300 15.1 35.1 46.9 325 14.9 50.8 32.3

[0041] CF₃CF═CFH is a mixture of cis and trans isomers. Small amounts ofother byproducts were present.

Example 2

[0042] Reaction of CF₃CF═CFH with HF

[0043] The reactor was charged with 15.2 g of fluorided alumina whichwas obtained by the exhaustive fluorination of gamma-alumina with HF asdescribed in U.S. Pat. No. 4,766,260. A flow of HF and CF₃CF═CFH in a4:1 molar ratio was started through the reactor. The contact time was 30seconds. The organic feed contained 85.3% CF₃CF═CFH, 13.6%trifluoroethylene and 0.8% CF₃CFHCHF₂ in addition to small amounts ofother components. Product analysis indicated the following. Temp. ° C.CF₃CH₂F CF₃CF═CFH CF₃CHFCHF₂ 250 14.0 85.1 0.8 300 14.0 74.8 1.0 35013.6 80.9 4.9 400 13.4 78.4 6.8 425 13.9 79.4 4.5

[0044] Small amounts of other byproducts were present.

Example 3

[0045] Reaction of a Mixture of CF₃CH═CF₂ and CF₃CF═CFH with HF

[0046] The reactor was charged with 6.3 g of acid washed carbon. It wasdried in a stream of nitrogen (25 mL/min) for about two hours at 175° C.prior to start of the reaction. The organic feed mixture consisted of47.3% CF₃CH═CF₂, 50.0% CF₃CF═CFH, 0.7% CF₃CFHCHF₂ and 0.4% CF₃CH₂CF₃ inaddition to small quantities of other products. The HF to total organicratio was 4:1 and the contact time was 15 seconds. Product analysisindicated the following. Temp. ° C. CF₃CH═CF₂ CF₃CF═CFH CF₃CFHCHF₂CF₃CH₂CF₃ 200 33.8 50.1 1.0 13.5 250  0.7 48.4 1.0 46.0

Example 4

[0047] Reaction of a Mixture of CF₃CH═CF₂ and CF₃CF═CFH with HF

[0048] The reactor was charged with 6.5 g of 10 weight percent chromiumchloride on carbon which was activated with HF according to the generalprocedure described above. The organic feed mixture consisted of 47.3%CF₃CH═CF₂, 50.0% CF₃CF═CFH, 0.7% CF₃CFHCHF₂ and 0.4% CF₃CH₂CF₃ inaddition to small quantities of other products. The HF to total organicratio was 4:1 and the contact time was 15 seconds. Product analysisindicated the following. Temp. ° C. CF₃CH═CF₂ CF₃CF═CFH CF₃CFHCHF₂CF₃CH₂CF₃ 175 41.6 49.9 1.1  6.0 200 25.6 49.1 1.6 21.9 225  7.2 48.32.0 40.5 250  1.0 46.4 2.3 48.6

Example 5

[0049] Reaction of a Mixture of CF₃CH═CF₂ and CF₃CF═CFH with HF

[0050] The reactor was charged with 19.4 g of chromium oxide which wasactivated with HF according to the general procedure described above.The organic feed mixture consisted of 47.4% CF₃CH═CF₂, 50.1% CF₃CF═CFH,0.7% CF₃CFHCHF₂ and 0.4% CF₃CH₂CF₃ in addition to small quantities ofother products. The HF to total organic ratio was 4:1 and the contacttime was 15 seconds. Product analysis indicated the following. Temp. °C. CF₃CH═CF₂ CF₃CF═CFH CF₃CFHCHF₂ CF₃CH₂CF₃ 125 45.6 50.4 1.0  2.1 15037.7 50.2 1.3  9.9 175  8.6 49.0 3.6 37.9 200  0.1 46.2 4.5 48.1 225 0.0 46.2 4.6 48.4 250  0.0 45.6 4.8 48.3 279  0.0 43.3 6.8 48.4 302 0.0 36.1 13.6  48.3 326  0.0 29.1 19.5  49.3 350  0.0 33.6 15.8  48.4

[0051] There were small amounts of other minor by-products present.

[0052] Examination of the data shown in Example 5 indicates thatreaction at a lower temperature produces CF₃CH₂CF₃ and reaction at ahigher temperature produces CF₃CFHCHF₂ thus showing that the samecatalyst can be used in a two stage reaction, one stage operating at alower temperature and one stage operating at a higher temperature.

What is claimed is:
 1. A process for producing CF₃CHFCHF₂, comprising:reacting CF₃CF═CHF with HF at an elevated temperature over a catalystselected from the group consisting of aluminum fluoride, fluoridedalumina, metals on aluminum fluoride, metals on fluorided alumina andcatalysts comprising trivalent chromium.
 2. The process of claim 1wherein CF₃CF═CHF is produced by dehydrofluorinating CF₃CF₂CH₂F.
 3. Theprocess of claim 1 wherein a starting mixture comprising CF₃CF═CHF andCF₃CH═CF₂ is reacted with HF at an elevated temperature over afluorination catalyst to produce CF₃CH₂CF₃ from said CF₃CH═CF₂.
 4. Theprocess of claim 3 wherein the starting mixture is reacted at anelevated temperature over a catalyst consisting essentially of carbon, acatalyst consisting essentially of metal halides on carbon, a catalystconsisting essentially of Cr₂O₃, or mixtures thereof, provided that whenCr₂O₃ is present the temperature is about 250° C. or less, to provide aproduct mixture containing CF₃CH₂CF₃ and unreacted CF₃CF═CFH; whereinthe CF₃CH₂CF₃ is separated from CF₃CF═CHF in the product mixture; andwherein CF₃CF═CHF from the product mixture is reacted with HF.
 5. Theprocess of claim 4 wherein the starting mixture is reacted with HF overa catalyst consisting essentially of carbon.
 6. The process of claim 4where CF₃CF═CHF from the product mixture is reacted with HF overchromium oxide prepared by the pyrolysis of ammonium dichromate.
 7. Amethod for enriching CF₃CF═CHF from a starting mixture containingCF₃CF═CHF and CF₃CH═CF₂ comprising: reacting said starting mixture withHF at an elevated temperature over a catalyst consisting essentially ofcarbon, a catalyst consisting essentially of metal halides supported oncarbon, a catalyst consisting essentially of Cr₂O₃, or mixtures thereof,provided that when Cr₂O₃ is present the temperature is about 250° C. orless, to provide a product mixture containing CF₃CH₂CF₃ and unreactedCF₃CF═CHF wherein the mole ratio of CF₃CF═CHF to CF₃CH═CF₂ is greaterthan the ratio thereof in the staring material.
 8. A compositionconsisting essentially of hydrogen fluoride in combination with aneffective amount of a compound selected from the group consisting ofCF₃CHFCHF₂ and CF₃CH₂CF₃ to form an azeotrope or azeotrope-likecomposition with hydrogen fluoride, said composition containing fromabout 31 to 60 mole percent CF₃CFHCHF₂ or from about 41 to 63 molepercent CF₃CH₂CF₃.
 9. The composition of claim 8 consisting essentiallyof about 69 to 40 mole percent HF and about 31 to 60 mole percentCF₃CHFCHF₂, said composition having a boiling point from about −25° C.at 32 kPa to about 100° C. at 2500 kPa.
 10. The composition of claim 8consisting essentially of from about 59 to 37 mole percent HF and about31 to 63 CF₃CH₂CF₃, said composition having a boiling point from about−25° C. at 44 kPa to about 100° C. at 2900 kPa.